What if it rains? Are all seat in covered?

Yes the part where the seats is are covered but not the lawn part

The lawn is not covered, but the reserved seating and pit areas are covered. Having been at a concert here when it rains, they do move those on the lawn inside the facility if there is severe weather.

Seats are covered directly overhead. Rain could still get you if you're in the back of it's coming that direction. Lawn is not covered at all. Just got completely drenched last weekend at NF's concert during tornado warning, tons of fun though. Makes it memorable!